Bad Air/ Fuel mixture sensor warning for ALL Yaris owners

[eric81]

I highly advise that anyone who owns a Yaris and wants to replace the exhaust header, please read this. Anyone who has already replaced their exhaust header can verify. The factory A/F mixture sensor that is "screwed" into the manifold by the factory is cross threaded, and therefore won't come out. I actually broke mine in half trying to get it out. So, I bought an aftermarket eBay brand A/F sensor on eBay (duh) for a "great" price, and it turns out it almost cost me a new engine. I thought the power was starting to slide a little bit, especially for having a CAI, Megan header, and 3A racing muffler (not really a muffler, as it doesn't muffle or restrict air in any way at all). After I replaced the header, the check engine light wouldn't turn off, and I was running rich all the time, so I forked over the cash to NST (great prices and products... highly recommended) and they shipped me a replacement A/F sensor, and the light went out right away. What I hadn't realized was the damage caused to my engine in that 500 miles I drove with the car running so rich. I just pulled the plugs to check them, and they were burnt to a crisp. I bought replacement ones for about $30 for the set of 4 (yes, I stuck with Iridium's) and set the gap to 44, and started the car. Black and grey smoke came flying out. I also bought some piston, ring, and valve cleaner that I will be using the next time I fill up. My neighbor swears by it, so we will see. Anyways, from my understanding, one or two more thousand miles and I would have just cooked the engine right off. Please plan to buy a new A/F sensor when you buy a new header. And check the plugs soon after the replacement, just to make sure. Drive on!

[m911gt]

i can personally confirm this! you are the third person other than myself who has experienced the cross threaded AF sensor.

[Shroomster]

LIVE AND LEARN I GUESS

I would hope going beyond changing oil in a car, people would take the time to research the "mods they are doing" there is a reason after all they are called modifications.....
it will save you time and money in the long run if you do some research on what exactly you are repairing when a part breaks and what that broken part affects

but I don't know your situation and if it's like me you probably have your car as a daily driver and couldn't afford for it to be down for too long....which is why you did what you did I dunno....

I'm not criticizing you at all nor am I attempting to sound combative towards you, please don't take offense.

[Reddog99]

Are you guys talking about the oxygen sensor?

[BailOut]

Excuse me while I go hug my perfectly working stock ehxaust system.

[Reddog99]

So the exhaust has an oxygen sensor AND an "A/F mixture sensor"?

Here I am thinking that the oxygen sensor IS an A/F mixture sensor.

[cleong]

The sensor is an O2 (oxygen) sensor and is matched to fuel signals sent by the ECU to the injectors.

Sounds like a clumsy pair of hands that reinstalled the O2 sensor. A bit of grease on the threads always makes things easier. And you ignored the dashboard warnings - a car wouldn't start throwing codes for no reason. Mine didn't so much as flicker when it started up, and I never saw a CEL after months of driving around with my header and exhaust install.

Its another reason to track your car's fuel consumption and other vital fluids. When it starts consuming too much fuel, engine oil, or coolant, you should start looking for the problem, or letting a mechanic have a look at it.

[eric81]

I saw the codes, and started asking lots of questions to everyone on Yaris World. (I was ergatzke before.) I knew the sensor was wrong, just didn't understand what it was doing to the engine. The car ran rich for a long time, and was very fast and loud. Thought it was just a really nice header. Now I know it was because the A/F sensor (which reads how much fuel is being burned compared to how much is not) was not right. The O2 sensor reads how clean or consentrated the oxygen and carbon mixtures are coming from the engine. That part is for economical reasons, like saving trees and what not. (that is right, isn't it?) I also thought part of the CEL (check engine light) problem was that I was letting way more air into the engine with a CAI (cold air intake) and letting far more out with an exhaust header and racing muffler. I am letting the engine breathe far better, but it is not near enough to throw a CEL. The problem is fixed, and I am once again running nice and smooth. I changed plugs and it is running better, and used Lucas Engine Cleaner to clean the rings, pistons, and valves. It seems to have worked because my drive to and from Portland from Olympia was easy, and I was KILLING IT on the highway. Hit 100 once with ease. (Yes, that is 100 MPH, not 100 KPH) I am not a certified mechanic, but I did stay in a Holiday In Express once, and I can tell you this engine is fairly simple, and anyone can figure out that if they did something to the engine, and the CEL turns on, it is probably their fault.

And I don't mind people being a little offensive, but thanks for the clarification.

[ddongbap]

Actually, a car running rich doesn't really do much. The darkness is actually improperly burnt fuel. You'd be in trouble if the spark plugs were white-ish. You really weren't in TOO much trouble by a rich running car.

[eric81]

From my understanding, many a people have thrown pistons that way. But our cars are pretty low on the power, so you are probably right. Still, it was pretty bad in my engine. And it smoked BAD when I put the new plugs in. It is all nice now. I will check the plugs in about 2 or 3 more tanks. I will also post a pic of one of the bad plugs here tomorrow sometime. It is WAY burnt up. All black and stuff. My neighbor even felt bad for me.

[1stToyota]

Originally Posted by Reddog99

So the exhaust has an oxygen sensor AND an "A/F mixture sensor"?

Here I am thinking that the oxygen sensor IS an A/F mixture sensor.

Toyota calls their upstream O2 sensor an A/F mixture sensor.

[cali yaris]

oyota calls their upstream O2 sensor an A/F mixture sensor.

Correct, and it's a very unusual 0-5v sensor, made by Denso for Toyota OEM. No one else makes it, and you have to get it from Toyota (or a salvage yard )

The rear one, between the cats, is an O2, however.

My header install went fine -- no cross-threading and no CEL's.

[1stToyota]

Originally Posted by cali yaris

Correct, and it's a very unusual 0-5v sensor, made by Denso for Toyota OEM. No one else makes it, and you have to get it from Toyota (or a salvage yard )

The rear one, between the cats, is an O2, however.

My header install went fine -- no cross-threading and no CEL's.

I bought a Bosch replacement not too long ago. No comeback yet...knocks wood

[ChinoCharles]

I helped test that Megan header when it first came out and had to install and uninstall it multiple times. Never had a problem.

[eric81]

Maybe it is just the 08's, or just a certain series of the Yaris, or just a certain month or some other group.

[TheSilkySmooth]

A zero-to-5 V is a wide range Lambda (mixture) sensor which is still technically an oxygen sensor. It just has the ability to read lean and rich conditions which a std O2 can only read (perform a step function form near zero volt output to 1+v output at rich) so the EC unit can run at stoichiometric or "perfect mixture". The Car swith the old system are constantly varying between lean and rich to find the centre. On the 0-5V, Toyota can then run the car a bit lean at light / throttle light load. This is like what a dyno tune shop uses for a sensor. They Used to be big bucks and I though aonly used on the Prius - but the tech must have trickeled down the inexpensive Yaris. Now the mystery of the awesome gas mileage (with my dad driving at least) is solved! Yeah, dad gets 40 and sis gets 35!

sonja's bro (Our family, we got to get separate logins! but we love the Yaris World!)

[kou]

any time you have to change an o2 sensor i have found you should heat the area of the pipe/manifold around it,this usualy gets even the rusted ones out.

[Return of the Yarii]

I have an 07 Sedan and mine was crossthreaded, found out when I did DC header install, bought a new one from Ken @ Sparks. Its listed in the classifieds along w/the header.

It is indeed an Air/Fuel Sensor, the O2 sensor is downstream

*pending sale of A/F Sensor to member on the board*